Immunosuppressive treatment in allogeneic transplantation is an effective way to control allograft rejection. But unfortunately it can cause serious side effects, such as infections or malignancies. Cell therapeutic approaches for induction of specific tolerance are on the rise and may have fewer side effects. We observed that monocytes or peripheral blood mononuclear cells (PBMC) of healthy persons after culture with dendritic cell-inducing cytokines and differentiation blockade with the chemotherapeutic drug mitomycin C (MMC) show the ability to suppress allogeneic T cell responses. Interestingly these cells resemble morphologically as well as phenotypically myeloid-derived suppressor cells (MDSC) which occur in cancer patients impairing the anti-tumor immunity. FACS- and gene expression analyses of these MMC incubated blood cells revealed downregulation of the immunostimulatory cell surface molecules CD80, CD83, CD86 and HLA-DR, and upregulated transcription of immunosuppressive and pro-apoptotic genes such as iNOS, arginase-1, IL-10, COX2, TGF-β, placental growth factor, immunoglobulin-like transcript 3, adrenomedullin, SMAD5, LRDD and of the transcription factor C/EBPβ. For use in preclinical transplantation models in vitro culture of MMC treated donor-derived blood cells with dendritic-cell inducing cytokines was not applicable and was therefore omitted. The tolerance inducing properties of donor-derived MMC incubated blood cells were investigated in two different animal models of solid organ transplantation. When injected into rats, donor-derived PBMC incubated with MMC strongly prolonged heart allograft survival. Suppression of rejection was donor-specific. Recipients showed an increased number of CD4+CD25+FoxP3+ regulatory T-cells and tolerance could be transferred to syngeneic recipients with blood or spleen cells. Donor-derived MMC incubated blood cells also prolonged kidney allograft survival in pigs. Furthermore, in a first clinical use a 6-year-old girl with relapse of acute lymphoblastic leukemia and imminent rejection of a third haploidentical stem cell transplant received donor-derived CD3/CD19-depleted peripheral blood stem cells, which have been treated in vitro with MMC, in order to prohibit graft rejection. We describe a simple method for in vitro generation of tolerance inducing donor-derived blood cells for potential use in clinical organ transplantation.
No relevant conflicts of interest to declare.
